An interconnector line of thin film used as a gate line and a source electrode bus-line for a TFT drive type LCD is generally produced by a sputtering method. As materials for such an interconnector line of thin film, Cr, Ti, Mo, Mo--Ta and the like have been used. But, with the enlargement of an LCD screen size, a low-resistance interconnector line of thin film is being needed. For example, a large LCD of 10 inches or more is required to have a low resistant interconnector line of 10 .mu..OMEGA.cm or below. Accordingly, a low-resistance Al is attracting attention as an interconnector line of thin film for a gate line, a signal line and the like.
With the Al interconnector line of thin film, low-resistance interconnector line can be achieved, but the Al interconnector line of thin film has a problem of having protrusions called hillocks due to heating at about 473 to 773K by a heat treatment and a CVD process after interconnector line. In a process of releasing a stress of the Al film involved in heating, Al atoms spread along, for example, grain boundaries. Protrusions (hillocks) are caused involved in the spreading of Al atoms. When the protrusions are formed on the Al interconnector line, an adverse effect is caused in the subsequent process.
Therefore, it is attempted to add a very small amount of metallic elements, e.g., Fe, Co, Ni, Ru, Rh and Ir or rare earth metallic elements such as Y, La and Nd (see Japanese Patent Application Laid-Open Publication No. Hei 7-45555). Specifically, an Al interconnector line of thin film is formed using an Al target having a very small amount of such metallic elements added. The above-described metallic elements form an intermetallic compound in cooperation with Al and function as a trap material for Al. Thus, the above-described hillocks can be restrained from being occurred.
And, where the Al interconnector line is applied to source electrode bus-lines of the LCD, the Al interconnector line is stacked with an ITO electrode. When the stacked film of the Al interconnector line and the ITO electrode is immersed in an alkali solution such as a developing solution used in a patterning process, an electrochemical reaction is caused at portions where the Al interconnector line and the ITO electrode are directly contacted. The electrochemical reaction between the Al interconnector line and the ITO electrode is caused because the standard electrode potential of Al is lower than that of the ITO. Electrons are moved between the Al interconnector line and the ITO electrode due to the electrochemical reaction, resulting in a problem that the ITO electrode is colored (e.g., blackening) by being reduced and the Al interconnector line is conversely oxidized to lower electrical characteristics.
In connection with the problem due to the electrochemical reaction between the Al interconnector line and the ITO electrode described above, it is also studied to add various types of metallic elements to the Al interconnector line. In such a case, the Al target with an very small amount of metallic elements added is also used to form the Al interconnector line of thin film containing a very small amount of metallic elements.
However, the above-described Al interconnector line of thin film containing a very small amount of metallic elements suppress the diffusion of Al and the electrochemical reaction with the ITO electrode, but there are problems that the produced intermetallic compound and the added metallic elements cause an adverse effect on the etching property and sputtering property of the Al interconnector line.
Specifically, when dry etching such as CDE (chemical dry etching) and RIE (reactive ion etching) or wet etching is made on the above-described Al interconnector line of thin film, a lot of undissolved remains called residues are produced, causing a serious difficulty in forming an interconnector line network. The added metallic elements and the produced intermetallic compounds are the causes of the residues after etching as described above. And, the Al target containing the metallic elements described above causes a large amount of dust while sputtering, causing a difficulty in forming a good and fine interconnector line network.
Therefore, in the Al target and Al interconnector line of thin film used to form low-resistance interconnector line, it is a subject to restrain the occurrence of residues in etching and the occurrence of dust in sputtering in addition to suppression of the occurrence of hillocks due to the diffusion of Al and the electrochemical reaction with the ITO electrode.
And, in connection with the suppression of the electrochemical reaction between the Al interconnector line and the ITO electrode, it is desired to improve an effect upon reducing the added amount of electrical elements. The electrochemical reaction between the Al interconnector line and the ITO electrode is also studied to be suppressed by having a stacked structure of the Al interconnector line and an Mo film or the like. But, such a stacked film involves a complex LCD structure and a high cost, so that it is desired to suppress the electrochemical reaction with the ITO electrode by the Al interconnector line having a single layered structure.
The above-described subject is not limited to the Al interconnector line of thin film used for the gate line and signal line of the LCD. For example, where the Al interconnector line is applied to a typical semiconductor device such as VLSI and ULSI, electromigration is a problem. The above-described metallic elements have an effect to suppress the electromigration (see Japanese Patent Application Laid-Open Publication No. Sho 62-228446 and Japanese Patent Publication No. Hei 4-48854), but there is a problem that residues are caused in etching and dust is caused in sputtering as in the case of the LCD. And, the above-described subject is also an issue in a surface acoustic wave apparatus such as a surface acoustic wave oscillator (SAW), an electronic part using SAW (SAW device), or interconnector line and electrodes for a thermal printer head (TPH).
An object of the invention is to provide a low-resistance interconnector line of thin film with the occurrence of hillocks and etching residues prevented and a sputter target which can form the interconnector line of thin film with good reproducibility with the occurrence of dust in sputtering suppressed. Another object of the invention is to provide a low-resistance interconnector line of thin film which has the electrochemical reaction with the ITO or the like and the occurrence of the etching residues prevented and a sputter target with the occurrence of dust in sputtering suppressed. Besides, it aims to provide an electronic part using such a interconnector line of thin film.